In recent years, with the rapid development of display technology, early cathode ray tube (CRT) display has also been replaced by active-matrix display, e.g., active-matrix liquid crystal display (AMLCD) and active-matrix organic light-emitting diode (AMOLED) display. In these active-matrix displays, TFT, taken as a core device of active-matrix display technology, receives great attention and is widely applied.
According to different materials of active layers in TFTs, the TFTs may be divided into amorphous silicon (a-Si) TFT, polysilicon (poly-Si) TFT, metal oxide TFT, etc. The metal oxide TFT and the poly-Si TFT have higher mobility than the a-Si TFT. Compared with the poly-Si TFT, the manufacturing process of the metal oxide TFT is simpler as there is no limit on devices for ion implantation and laser crystallization. Therefore, the metal oxide TFT is widely applied in liquid crystal displays (LCDs), organic light-emitting diode (OLED) displays and polymer light-emitting diode (PLED) displays.